In relation to conventional tapered roller bearings, various resin cages have been proposed (see, e.g., Patent Documents 1 to 4). For example, according to a cage 101 disclosed in Patent Document 1, as shown in FIGS. 25(a) and 25(b), a radial dimension of a bar portion 102 is enlarged to reduce a volume of space inside a tapered roller bearing 100, thereby reducing an amount of lubricating oil inside the bearing to lower an agitation resistance. Further, in an inner peripheral surface side of the bar portions 102, guide grooves 103 whose diameter is enlarged from a small diameter annular portion to a large diameter annular portion are provided to smooth the flow of the lubricating oil, reduce the amount of lubricating oil staying in the bearing and to improve heat-seizure resistance. Such a structure is similarly provided in a tapered roller bearing cage disclosed in Patent Document 2.
Further, according to this cage 101, opening widths W1, W2 in the circumferential direction in an outer peripheral side and an inner peripheral side of each pocket 104 are respectively smaller than a diameter R of a tapered roller 105 in a corresponding position to hold the tapered roller 105 in an embracing manner, so that the tapered roller 105 is prevented from falling from the cage 101. Such a structure is similarly provided in tapered roller bearing resin cages disclosed in Patent Documents 3 and 4.